Wastewater treatment device and wastewater treatment method

ABSTRACT

A wastewater treatment device has: an ozone generator which supplies ozone; a mixer which mixes ozone supplied from the ozone generator with wastewater and supplies ozone mixed wastewater; an ozone oxidation unit which progresses ozone oxidation in the ozone mixed wastewater while passing the ozone mixed wastewater therethrough and discharges wastewater in which the ozone has been consumed; a biological treatment unit which performs biological treatment on the wastewater discharged from the ozone oxidation unit using microorganisms; and an adjusting device which adjusts the amount of ozone to be mixed with the wastewater by the mixer so that ozone in an amount that inhibits the microorganisms of the biological treatment unit does not remain in the wastewater discharged from the ozone oxidation unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S.application Ser. No. 16/166,311, filed on Oct. 22, 2018, which is acontinuation application of International Application No.PCT/JP2017/027528, filed on Jul. 28, 2017, which claims priority toChinese Patent Application No. 201610609203.X, filed on Jul. 28, 2016,the entire contents of which are incorporated by reference herein.

BACKGROUND Technical Field

The present disclosure relates to a wastewater treatment device and awastewater treatment method capable of performing advanced treatment ofindustrial wastewater utilizing ozone oxidation reaction and biologicaltreatment using microorganisms.

Description of the Related Art

Industrial wastewater (wastewater from chemical industry, agriculture,printing factories, dyeing plants, and the like) contains a large amountof persistent organic pollutants, and in conventional biologicaltreatment processes, the persistent organic pollutants still remain interminal water of biological treatment. Therefore, since the terminalwater of the biological treatment of the industrial wastewater does notreach effluent standards, pollutants cannot be completely removed afterintroduction into municipal wastewater treatment plants, which adverselyaffects the municipal wastewater treatment plants. Thus, the treatmentof highly polluted industrial wastewater is a global and important issuethat the processing of industrial wastewater currently faces.

Biodegradability by biological treatment of terminal drainage ofindustrial wastewater is extremely different depending on wastewater,and it is difficult to process the terminal wastewater using thebiological treatment directly. In a practical strategy, the treatmentprocess currently mainly used is advanced treatment includingcoagulation sedimentation, adsorption, and chemical oxidation.

In order to realize the advanced wastewater treatment of the industrialwastewater, technologies of treating wastewater by combining theoxidation reaction or the photochemical reaction by ultraviolet lighthave been proposed. Japanese Patent Application Laid-open No.2015-128751 (Publication Document 1 below) discloses wastewatertreatment which is a combination of the biological treatment with Fentontreatment which is oxidation treatment.

Further, ozone oxidation is a more general technology in the advancedtreatment of the terminal water by the biological treatment of theindustrial wastewater. However, when the ozone oxidation technology isused alone, treatment cost is frequently increased to realize theadvanced treatment of the industrial wastewater. For this reason, thecombination of the ozone oxidation technology with the biologicaltreatment has been studied to reduce the treatment costs. JapanesePatent Application Laid-open No. 2015-226889 (Publication Document 2below) discloses treatment of a liquid containing an amine-based organiccompound, obtained by combining the oxidation treatment for introducingan oxidizing agent to decompose the amine-based organic compound withthe biological treatment, and discloses that ozone is used as theoxidizing agent.

DOCUMENTS LIST

Publication Document 1: Japanese Patent Application Laid-open No.2015-128751

Publication Document 2: Japanese Patent Application Laid-open No.2015-226889

BRIEF SUMMARY

However, the Fenton treatment utilized in the above-mentionedPublication Document 1 requires much time and labor because it has anincreased number of processes. On the other hand, since the ozoneoxidation treatment utilized in the above-mentioned Publication Document2 has low solubility of ozone in water and weak oxidizing ability ofozone, the ozone oxidation treatment has drawbacks such as a slow masstransfer rate between gas and liquid and low ozone utilizationefficiency. Further, in Publication Document 2, since the ozoneoxidation treatment is carried out at a pH significantly different fromthe subsequent biological treatment, a process of adjusting the pH atthe time of shifting to the biological treatment is necessary, and thetreatment cost is increased. Furthermore, even when unused ozone isdischarged from wastewater, the ozone utilization efficiency is lowered.

Further, in any of the above-described wastewater treatments, aerationis performed in order to activate treatment with aerobic microorganisms.However, the aeration of wastewater requires power, and, from theviewpoint of energy consumption, it is preferred to perform thewastewater treatment without using the aeration.

The present disclosure has been made in view of the above-describedproblems, and it is an object of the present invention to provide awastewater treatment device and a wastewater treatment method capable ofpreventing an inhibition of biological treatment while enjoyingadvantages of wastewater treatment by ozone oxidation, reducingwastewater treatment costs, and realizing excellent treatment by asimple process.

According to an aspect of the present disclosure, a wastewater treatmentdevice is summarized to include: an ozone generator which suppliesozone; a mixer which mixes ozone supplied from the ozone generator withwastewater and supplies ozone mixed wastewater; an ozone oxidation unitwhich progresses ozone oxidation in the ozone mixed wastewater whilepassing the ozone mixed wastewater therethrough and dischargeswastewater in which the ozone has been consumed; a biological treatmentunit which has microorganisms for biological treatment and performs thebiological treatment on the wastewater discharged from the ozoneoxidation unit using the microorganisms; and an adjusting device whichadjusts the amount of ozone to be mixed with the wastewater by the mixerso that ozone in an amount that inhibits the microorganisms of thebiological treatment unit does not remain in the wastewater dischargedfrom the ozone oxidation unit.

It is suitable that the adjusting device includes: a measuring devicewhich measures the amount of ozone in the wastewater discharged from theozone oxidation unit; and a regulating valve capable of regulating theamount of ozone to be mixed with the wastewater by the mixer, and theregulating valve is adjusted based on the measurement by the measuringdevice in such a manner that the amount of ozone in the wastewater islower than a level at which the microorganisms are inhibited.

The wastewater treatment device may further include: a release passagefor avoiding the supply of the wastewater to the biological treatmentunit when the ozone remains in the wastewater discharged from the ozoneoxidation unit; and a control valve which stops the supply of thewastewater to the biological treatment unit when the amount of ozone inthe wastewater is equal to or higher than the level at which themicroorganisms are inhibited, based on the measurement by the measuringdevice. The release passage may be a return passage capable of supplyingthe wastewater discharged from the ozone oxidation unit to the mixer,and the wastewater may flow through the return passage when the supplyof the wastewater to the biological treatment unit is stopped by thecontrol valve.

It is suitable that the mixer includes a bubble generator, and ozone isdispersed in the ozone mixed wastewater in a state of bubble. It issuitable that the bubble generator is a microbubble generator whichgenerates fine bubbles having a bubble diameter of 10 to 50 μm. Theozone oxidation unit may have a catalyst that promotes an ozoneoxidation reaction, and the ozone oxidation unit may be configured in amultistage structure in which a plurality of catalyst beds on which thecatalyst is supported are stacked in a vertical direction, and may beconfigured so that the ozone mixed wastewater may sequentially passthrough the plurality of catalyst beds while being introduced from abottom part of the ozone oxidation unit and rising toward a top part ofthe ozone oxidation unit.

When a difference in height between the biological treatment unit andthe ozone oxidation unit is provided so that a water level in thebiological treatment unit is lower than that in the ozone oxidationunit, and the wastewater of the ozone oxidation unit is supplied to thebiological treatment unit using a gravity action due to the differencein height, it is suitable in terms of reducing operating energy. Thewastewater treatment device may further include an ozone decomposingdevice which decomposes ozone remaining in the wastewater dischargedfrom the ozone oxidation unit when ozone remains in the wastewaterdischarged from the ozone oxidation unit.

In addition, according to an aspect of the present disclosure, thewastewater treatment method is summarized to include: ozone generationthat supplies ozone; mixing preparation for mixing the ozone supplied bythe ozone generation with wastewater to supply ozone mixed wastewater;ozone oxidation treatment in which ozone oxidation is allowed to proceedin the ozone mixed wastewater, to discharge the wastewater in which theozone has been consumed; and biological treatment in which thewastewater after the ozone oxidation treatment is biologically treatedwith microorganisms, wherein an amount of ozone mixed with thewastewater in the mixing preparation is adjusted so that ozone in anamount that inhibits the microorganisms of the biological treatment doesnot remain in the wastewater discharged from the ozone oxidationtreatment.

A ratio of ozone to be mixed with the wastewater may be adjustedaccording to a flow rate of the wastewater supplied to the ozoneoxidation treatment and water quality of the wastewater so that anappropriate amount of ozone is mixed with the wastewater in the mixingpreparation. It is suitable for application to an advanced treatment fortreating industrial wastewater containing a persistent organicsubstance.

According to the present disclosure, it is possible to provide awastewater treatment device capable of improving the ozone utilizationrate to enhance oxidation ability, and improving the removal efficiencyof persistent chemical substances, and it is also possible tosufficiently supply the biological treatment with oxygen withoutperforming the aeration by using dissolved oxygen generated after theozone reaction, thereby reducing operating costs required for wastewatertreatment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram showing a basicconfiguration of a wastewater treatment device according to the presentdisclosure.

FIG. 2 is a schematic configuration diagram showing an embodiment of thewastewater treatment device based on the basic configuration of FIG. 1.

FIG. 3 is a schematic configuration diagram showing another embodimentof the wastewater treatment device.

FIG. 4 is a schematic diagram showing a modified example of a part ofthe wastewater treatment device according to the present disclosure.

FIG. 5 is a schematic diagram showing another modified example of a partof the wastewater treatment device according to the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described in detail belowwith reference to the drawings. Here, it is noted that dimensions,materials, other specific numerical values, and the like shown in theembodiments are merely examples for facilitating understanding of theinvention, and do not limit the present invention unless otherwisenoted. In addition, in the specification and the drawings of the presentapplication, elements having substantially the same function andconfiguration are denoted by the same reference numerals, and redundantexplanations thereof are omitted and elements not directly related tothe present invention are not shown.

Industrial wastewater contains high concentrations of organicpollutants, and purification by biological treatment alone causes anexcessive burden on microorganisms. In addition, since the industrialwastewater contains a large amount of organic substances which arehardly decomposed by the microorganisms, the industrial wastewater isnot sufficiently purified and therefore the persistent organicsubstances may remain. On the other hand, since ozone oxidation, whichis a chemical treatment, can decompose larger organic molecules withless degradability into smaller organic molecules, it is possible toimprove the biodegradability of the industrial wastewater by applyingozone oxidation technologies to the industrial wastewater to remove apart of the organic pollutants, such that the burden on themicroorganisms in the biological treatment can be reduced. Inparticular, the ozone oxidation is effective for decomposition orlowering of molecular weight of compounds having an amino group, achloro group, a nitro group, a sulfo group and the like; an ethercompound, an unsaturated compound, an aromatic compound, a cycliccompound, and the like. For example, the aromatic compound having thenitro group can be decomposed into saturated hydrocarbon and ammonianitrogen. In the present disclosure, ozone mixed wastewater (mixture inwhich ozone is dispersed in wastewater) which is mixed and prepared by amixer is introduced into an ozone oxidation unit to advance the ozoneoxidation reaction (ozone oxidation treatment). Then the wastewater inwhich the ozone has been consumed is subjected to the biologicaltreatment with the microorganisms in a biological tank. However, sincethe ozone inhibits growth and activity of the microorganisms and makesthe progress of the biological treatment difficult, it is necessary toavoid the introduction of unused residual ozone into biologicaltreatment along with the wastewater that has been subjected to the ozoneoxidization treatment.

The wastewater treatment device shown in FIG. 1 includes an ozonegenerator 1, a microbubble generator 2, a suction pump 3, an ozoneoxidation unit 4, and a biological treatment unit 5. The microbubblegenerator 2 functions as a mixer of ozone and wastewater, and dispersesthe ozone in the form of fine microbubbles in the wastewater. The ozoneoxidation unit 4 is configured as an airtight pressure vessel, and has aplurality of catalyst beds C carrying a heterogeneous catalyst for anozone oxidation reaction therein. It is configured in a multistagestructure in which the plural catalyst beds C are stacked in a verticaldirection. The biological treatment unit 5 is configured in a multistagestructure in which a plurality of biological beds B having a biofilm onits surface respectively are arranged inside the biological treatmentunit 5.

In the wastewater treatment device of FIG. 1, the ozone generator 1generates ozone using pure oxygen as a raw material, in which the ozoneis introduced into microbubble generator 2. At the same time, thewastewater pumped by driving of the suction pump 3 is also supplied tothe microbubble generator 2 and mixed with ozone. In the microbubblegenerator 2, the ozone mixed wastewater in which the ozone is dispersedin a microbubble state is prepared. The ozone mixed wastewater flowsinto the ozone oxidation unit 4 from a bottom inlet. The supplied ozonemixed wastewater rises from a bottom part toward a top part of the ozoneoxidation unit 4, and sequentially passes through the plurality ofcatalyst beds C in the meantime, thereby promoting the ozone oxidationby contact with the catalyst. The wastewater in the ozone oxidation unit4 can be discharged under pressure. If the ozone is consumed by theozone oxidation reaction, oxygen is generated, and oxygen with highwater solubility is contained in the wastewater as dissolved oxygen. Thewastewater is circulated between the microbubble generator 2 and theozone oxidation unit 4, during which the wastewater is discharged fromthe ozone oxidation unit 4 depending on the amount of wastewatersupplied from the suction pump 3 and is supplied to the biologicaltreatment unit 5. The wastewater supplied to the biological treatmentunit 5 rises from the bottom part of the biological treatment unit 5toward the top part of the biological treatment unit 5, and passesthrough the biological beds B in the meantime. Since the wastewatersupplied to the biological treatment unit 5 contains high-concentrationdissolved oxygen, an aerobic reaction by microorganisms proceeds. As thetreatment proceeds, oxygen is consumed, and the treated water after thebiological treatment is discharged from an upper end of the biologicaltreatment unit 5.

Since the ozone inhibits the microorganisms and makes the progress ofthe biological treatment difficult, if the ozone remains in thewastewater that has been subjected to the ozone oxidation treatment, itis necessary to avoid the introduction into the biological treatmentunit 5. The wastewater treatment device and the wastewater treatmentmethod proposed in the present disclosure also include improvementsbased on such viewpoints, and it is possible to easily set conditionsfor the wastewater treatment and change them, and also to automaticallycontrol the treatment operations. The wastewater treatment device has anadjusting device for adjusting the amount of ozone to be mixed in thewastewater, and the amount of the ozone to be mixed with the wastewateris adjusted so that ozone in an amount that inhibits the microorganismsfor the biological treatment does not remain in the wastewater in whichthe ozone has been consumed in the ozone oxidation unit for progressingthe ozone oxidation reaction. Therefore, in the ozone mixed wastewaterprepared by the mixer, the amount of ozone to be mixed with thewastewater is appropriately adjusted. The ozone oxidation reaction inthe mixed wastewater is performed in the ozone oxidation unit (ozoneoxidation treatment), and then, when the wastewater which has consumedthe ozone is subjected to the biological treatment by microorganisms,ozone does not remain in such the amount that inhibits themicroorganisms for the biological treatment. When adjusting the mixedamount of the ozone, if ozone in an amount that inhibits themicroorganisms remains in the wastewater discharged from the ozoneoxidation treatment, supply of wastewater to the biological treatmentunit is avoided by utilizing the release passage to protect themicroorganisms from the residual ozone. In the configuration of FIG. 1,it is possible to return the wastewater to the microbubble generator 2from the top part of the ozone oxidation unit 4. When the water qualityof wastewater is not changed, it is possible to stably continue thewastewater treatment by adjusting the amount of ozone. Further, to copewith the change in the water quality or the treatment conditions, theabove-described adjustment is repeated and the supply of wastewater tothe biological treatment can be controlled by using the release passage.That is, when the ozone remains in the wastewater after the ozoneoxidation treatment, the supply of wastewater to the biologicaltreatment is suppressed so that the microorganisms for the biologicaltreatment are not inhibited by the remaining ozone. Based on the abovecontrol, improvements are made relating to the determination of suitabletreatment conditions of the wastewater, and relating to the monitoringand condition change while the wastewater treatment is stably continuedunder the determined treatment conditions. The release passage can beconfigured as a return passage through which the wastewater dischargedfrom the ozone oxidation unit can be directly supplied to the mixer.Alternatively, the release passage may be a return passage which isconfigured to be able to indirectly supply the wastewater dischargedfrom the ozone oxidation unit to the mixer via a wastewater source.

The concentration of ozone that inhibits microorganisms is changeddepending on the type and growth state of the used microorganisms, thecontact time with ozone, or the like. If the contact time is long, themicroorganisms are inhibited at a low ozone concentration. For example,nitrification activity is maintained to about 20 mg O₃/gSS for a shorttime contact in batch treatment using activated sludge, whereas incontinuous treatment using microorganisms obtained by ozoneacclimatization and preferential breeding of the activated sludge, thereis little influence to about 6 mg O₃/gSS. Therefore, the level of theozone concentration that inhibits microorganisms is set by investigatingozone resistance in the microorganisms to be used in advance.

When the ozone amount in wastewater is higher than or equal to the levelthat inhibits microorganisms, it is necessary to lower the mixed amountof ozone. As the adjusting device for adjusting the mixed amount ofozone, a measuring device for measuring the amount of ozone in thewastewater discharged from the ozone oxidation unit, and a regulatingvalve capable of regulating the amount of ozone which is supplied fromthe ozone generator to the mixer and mixed with the wastewater areprovided. The regulating valve is controlled so that the amount of ozoneto be mixed with the wastewater is reduced based on the measured valueof the ozone amount in the wastewater by the measuring device. At thistime, if the mixing ratio of ozone in the mixer is reduced correspondingto the difference in ozone concentration between the measured value ofthe ozone amount in the wastewater and the level inhibiting themicroorganisms, the mixing ratio of ozone in the mixer can efficientlyapproximate an appropriate value and the time required for theadjustment can be shortened.

In the case of avoiding the supply of wastewater to the biologicaltreatment unit, the control to suppress the supply of wastewater to thebiological treatment can be made by using a control valve which can stopthe supply of wastewater according to the situations of the wastewaterafter subjecting to the ozone oxidation treatment. Specifically, theozone amount in the wastewater discharged from the ozone oxidation unitis measured using the measuring device, and, based on the measuredvalue, the supply of wastewater to the biological treatment unit isstopped by the control valve when the ozone amount in the wastewater ishigher than or equal to the level that inhibits microorganisms. Theozone dissolved in the wastewater is decomposed in a relatively shorttime, but even a small amount of ozone may inhibit microorganisms. Thus,in the conventional wastewater treatment technology, bubbling or thelike is used, which promotes the release of ozone to the atmosphere. Inthe present disclosure, the supply to the biological treatment may beavoided only when the concentration of ozone in the wastewater is at thelevel that inhibits microorganisms. For the wastewater which is notsupplied to the biological treatment, the supply destination of thewastewater is switched, and thus the wastewater can be supplied by thereturn passage to the mixer directly or indirectly via the wastewatersource. The returned wastewater is prepared again as the ozone mixedwastewater, and the ozone oxidation treatment is repeated. In the supplyswitching of the wastewater, it is suitable to provide an on-off valvethat can intermittently direct the flow between the ozone oxidation unitand the biological treatment unit, and to operate it synchronously sothat the supply of wastewater is stopped when the on-off valve isclosed. Alternatively, the release passage (return passage) may beconfigured to be branched from a flow channel through which thewastewater is discharged from the ozone oxidation unit, and a directioncontrol valve is provided at a branch point to switch the flow channelthat communicates. As a modified example, the release passage branchedfrom the flow channel through which the wastewater is discharged fromthe ozone oxidation unit can be configured as a bypass path L6′ and thusan ozone decomposing device D can be provided on the bypass path (seeFIG. 4). The wastewater discharged from the ozone oxidation unit istemporarily prevented from being supplied to the biological treatmentunit by a switching valve V19 and the ozone remaining in the wastewateris decomposed by the ozone decomposing device. This wastewater can besupplied to the biological treatment unit. The ozone decomposing devicemay be according to any of methods such as adsorption decompositionmethod, heating decomposition method, catalytic decomposition methodusing alumina, silica or the like. In the case of using an ozonedecomposing apparatus D′ according to the heating decomposition method,the ozone decomposing apparatus D′ may be configured to be provided onthe channel L6 as shown in FIG. 5 to perform the decomposition bydetecting ozone using an ozone meter S6.

In the ozone oxidation of the wastewater, as the amount of organicpollutants is increased, the amount of ozone required for ozoneoxidation is increased. However, excessive ozone increases the residualozone amount of the wastewater after the ozone oxidation, and alsodecreases the ozone utilization efficiency in the ozone oxidation. Inthe evaluation using COD (chemical oxygen demand) as an index of organicpollutant concentration, when ozone is mixed with wastewater so that theozone/COD ratio is about 0.67 or less, the ozone utilization efficiencyof about 97.5% or more can be achieved and the amount of ozone remainingin the wastewater after the ozone oxidation also decreases. Therefore,the mixing ratio of ozone into wastewater is appropriately adjustedaccording to the COD of the wastewater to be treated, and the ozone/CODratio may be set to be about 0.67 mg/mg or less, preferably about 0.50mg/mg or less.

However, if ozone to be mixed is insufficient, though the ozoneutilization efficiency is high, persistent organic pollutants are notsufficiently decomposed and the burden of microorganisms in subsequentbiological treatment is likely to be increased. As a result, the optimummixing ratio of ozone is generally set to a ratio such that theozone/COD ratio is around 0.40 mg/mg. In order to set the optimum mixingratio more precisely, a ratio at which the ozone/COD ratio is somewhathigher, for example, a mixing ratio at which the ozone/COD ratio issomewhat larger than 0.4 mg/mg is set as an initial value to try thewastewater treatment, and the mixing ratio of ozone may be loweredgradually or stepwise so that the concentration of ozone remaining inthe wastewater after the ozone oxidation is lowered from a value higherthan or equal to the level of inhibiting microorganisms to a value lowerthan that level. Alternatively, with gradually increasing the mixingratio of ozone from a low value, the mixing ratio may be determined, atthe stage when the residual ozone is detected, to such a ratio that theresidual ozone concentration becomes less than the level inhibitingmicroorganisms.

The appropriate mixing ratio of ozone possibly changes depending on theratio of persistent organic substances occupied in the organicpollutants in wastewater. Basically, at least persistent organicsubstances in the wastewater may be decomposed in the ozone oxidationtreatment. In this respect, the mixing ratio of ozone may be generallyset so that the ozone/COD ratio is in a range of about 3 mg/mg or less,and wastewater whose COD is excessively high may be diluted in advancewith treated wastewater or the like as necessary. Therefore, in a simplemanner, the supply flow rate of ozone may be adjusted, depending on thewater quality (for example, COD) of the wastewater and the flow rate ofthe wastewater supplied to the ozone oxidation treatment, so that themixing ratio of ozone falls within the above-described appropriaterange. In wastewater that is subjected to the ozone oxidation at theappropriate mixing ratio, persistent organic substances aresatisfactorily decomposed and thus the burden of microorganisms in thesubsequent biological treatment is reduced, so that the microorganismsin the biological treatment well consumes easily decomposable organicsubstances. By the ozone oxidation, the decomposition and removal of theorganic pollutants can generally be achieved at a removal rate of about20 to 30% in terms of COD.

Ozone can be mixed with wastewater using a common gas-liquid mixer. Inorder to promote dissolution of ozone, subdivision and pressurizedsupply are effective. Therefore, in preparing the ozone mixedwastewater, it is preferable to bubble ozone using a bubble generatorand to disperse the ozone in wastewater in the form of fine bubbles. Thebubbling of ozone can be carried out by a mixer which mixes gas with aliquid by a gas-liquid shearing method, a foaming device which ejectsgas into a liquid from a minute ejection orifice, and an inline mixer(static mixer) which directly introduces gas into a flowing liquid, andthe like. It may be appropriately selected and used from the instrumentsor devices as described above. From the viewpoint of the reactioncontrol and the precision management, it is suitable that there are fewvariations in the size of bubbles. Further, when the bubbles are small,the gas-liquid contact area per volume becomes large, and thus ozonebecomes easy to dissolve in water. At the same time, the floating speedof bubbles is small and thus a residence time in water can be increased.Therefore, it is easy to increase the utilization efficiency of ozone.For this reason, it is convenient to use the microbubble generator asthe mixer. Microbubbles usually mean fine bubbles having a diameter ofabout 10 to 50 m. As described above, the microbubbles can significantlyimprove the gas-liquid mass transfer rate and transfer efficiency.Therefore, the supply of ozone using the microbubble generator canimprove the mass transfer and utilization efficiency of ozone in theozone oxidation treatment, and can greatly improve its effectiveness.

Since ozone easily reacts with organic compounds having a double bond,an activated aromatic group, an amino group, a sulfur-containing groupor the like and generates hydroxy radicals by the reaction, the ozoneoxidation relatively easily proceeds in industrial wastewater. However,in order to efficiently progress the wastewater treatment, it ispreferable to promote the ozone oxidation reaction. The ozone oxidationis promoted by addition of hydrogen peroxide, ultraviolet irradiation,or coexistence of a catalyst, whereby hydroxyl radicals or ozonide ionsgenerated from ozone contribute to the acceleration of oxidation.Therefore, if the promoting means as described above is used in theozone oxidation treatment, the treatment efficiency can be improved andthe treatment time can be shortened, which is useful for advancedtreatment of industrial wastewater. In particular, the use of thecatalyst is effective to reduce the treatment cost in long-termcontinuation of wastewater treatment. There are a homogeneous catalystand a heterogeneous catalyst as the catalyst. When the heterogeneouscatalyst is used, it is easy to separate the catalyst which is incontact with wastewater. For the above-mentioned reason, it isadvantageous to install a catalyst bed carrying the heterogeneouscatalyst in the ozone oxidation unit.

Examples of the heterogeneous catalysts for the ozone oxidation includemetal oxides, metal-supported oxides, platinum group metals, zeolites,activated carbon, and the like. Examples of the metal oxides includeFe₂O₃, CoO, MoO₃, MnO₂, SiO₂, Al₂O₃, TiO₂, and the like, and examples ofthe metal-supported oxide include those in which a metal such as Co, Cu,Pb, Ru, Pt, Pd and the like is supported on an oxide such as silica gel,titania and the like.

When the ozone is consumed by the ozone oxidation reaction, oxygen isgenerated, and the oxygen, having high water solubility, is contained inthe wastewater as dissolved oxygen. That is, as the ozone utilizationefficiency improves, the concentration of dissolved oxygen in wastewaterto be supplied to the biological treatment unit is increased, so thatthe aerobic treatment by microorganisms can proceed without aeration towastewater. In the present disclosure, a control mechanism is providedfor suppressing the supply of wastewater to the biological treatmentwhen ozone that inhibits microorganisms remains in the wastewater afterthe ozone oxidation treatment. Therefore, it is possible to increase theconcentration of dissolved oxygen in wastewater supplied to thebiological treatment by supplying the maximum amount of ozone to theextent that microorganisms for the biological treatment are notinhibited. This advantage is further enhanced by the supply of ozone asmicrobubbles and the use of a catalyst promoting the ozone oxidation. Inthe technology of the present disclosure, wastewater having aconcentration of dissolved oxygen (DO) of about 20 mg/L or more can besupplied to the biological treatment as wastewater after the ozoneoxidation treatment. This is sufficiently larger than the concentration(about 8 mg/L at maximum) obtained by ordinary aeration. Therefore,since the aeration is unnecessary in the biological treatment, energyconsumption accompanying the aeration can be eliminated and the cost ofwastewater treatment can be reduced. In addition, with supplying a highconcentration of oxygen, it is possible to increase a filling amount ofaerobic microorganisms for the biological treatment and increase thetreatment efficiency, which is also advantageous in this respect.

The biological treatment can proceed using the aerobic microorganismscommonly used for the biological treatment of organic wastewater, andexamples of the aerobic microorganisms include aerobic microorganismsconstituting activated sludge. Using oxygen generated from ozone, theaerobic treatment can be performed in wastewater without performing theaeration. By the aerobic treatment, a nitrogen component such as aminesis converted into ammonia nitrogen and nitrate nitrogen, a carboncomponent is converted into carbon dioxide and water, and a sulfurcomponent is converted into sulfate. In a treatment according to theactivated sludge method, anaerobic biological treatment proceeds inanoxic state after the aerobic biological treatment. Where themicroorganisms used for the biological treatment contain similaranaerobic microorganisms (or microorganisms having both aerobic andanaerobic properties), aerobic treatment and anaerobic treatment can becarried out. In that case, nitrate nitrogen is converted to nitrogengas.

From the viewpoint of continuously treating the wastewater, treatmentusing a biofilm is carried out in the biological treatment, in order toefficiently perform the contact and separation between the wastewaterand the microorganisms. The biofilm is formed by carrying microorganismson a carrier according to methods such as a rotating biological contactmethod, a trickling filter method, a catalytic oxidation method, anaerobic filter bed method, and the like. Using a porous body, a fibermaterial or the like as a carrier, the biological bed to be used can beformed by using the carrier and having microorganisms formed on thesurface thereof. It is efficient to construct a biological treatmentunit in a multistage structure composed of a plurality of biologicalbeds. The biological bed (biological filter) formed in a filter shapeusing a layered fiber material as the carrier can be handledconveniently.

In this way, by combining the ozone oxidation treatment with thebiological treatment, the supply of wastewater after the ozone oxidationtreatment is controlled so that the microorganisms in the biologicaltreatment are not inhibited, whereby the industrial wastewater ispossibly treated stably and continuously. The ozone utilization rate inthe ozone oxidation is high, and the persistent organic substances canbe efficiently decomposed by using the oxidation ability of ozone. Andthe biological treatment can efficiently proceed by utilizing thehigh-concentration oxygen generated from ozone.

An embodiment of a wastewater treatment device capable of carrying outthe wastewater treatment as described above will be described below withreference to the drawings. A wastewater treatment device 10 shown inFIG. 2 includes an ozone generator 1, a microbubble generator 2, asuction pump 3, an ozone oxidation unit 4, and a biological treatmentunit 5. In this embodiment, the microbubble generator 2 is adopted asthe mixer, but it is not limited to this adoption, and a commongas-liquid mixer may be used. The ozone oxidation unit 4 is configuredas an airtight pressure vessel and has a plurality of catalyst beds C inwhich a heterogeneous catalyst for ozone oxidation reaction issupported, and it has a multistage structure in which the plurality ofcatalyst beds C are stacked in the vertical direction. Inside thebiological treatment unit 5, a biological bed B having a biofilm on itssurface is disposed. Wastewater W is stored in a wastewater tank 6(wastewater source), and treated water W′ discharged from the biologicaltreatment unit 5 is stored in a post-treatment water tank 7.

The ozone generator 1 is connected to the microbubble generator 2through a flow channel L1, and the microbubble generator 2 is connectedto the suction pump 3 through flow channels L2, L3, and L4, and furtherconnected to a bottom inlet of the ozone oxidation unit 4 through a flowchannel L5. An upper end of the ozone oxidation unit 4 is connected tothe bottom part of the biological treatment unit 5 by a flow channel L6.

The ozone generator 1 generates ozone, using pure oxygen as a rawmaterial, and the ozone is introduced into the microbubble generator 2through the flow channel L1. At the same time, the wastewater W pumpedfrom the flow channel L2 by the driving of the suction pump 3 is alsosupplied to the microbubble generator 2 through the flow channel L3 andL4 and mixed with ozone. In the microbubble generator 2, the ozone mixedwastewater in which ozone is dispersed in a state of microbubbles isprepared. The ozone mixed wastewater flows into the ozone oxidation unit4 from the bottom inlet through the flow channel L5. In addition, a flowchannel L7 is provided to communicate a space above the catalyst bed Cin the ozone oxidation unit 4 with the flow channel L4, and such aconfiguration in which wastewater can return from the ozone oxidationunit 4 to the microbubble generator 2 through the flow channel L7 isformed. In other words, the flow channel L7 functions as a returnpassage through which wastewater directly returns from the ozoneoxidation unit 4 to the microbubble generator 2.

A flow rate control valve V1 capable of adjusting a flow rate of thewastewater W, a filter F1 for filtering the wastewater W, a flow meterS1 for detecting the flow rate of the wastewater W, and a one-way valveV2 for preventing a backflow of the wastewater W are provided on theflow channel L2. The flow rate control valve V1 is electricallyconnected to the flow meter S1 and is configured so that the flow ratein the flow channel L2 can be adjusted to a desired flow rate based onthe flow rate detected by the flow meter S1. A flow rate control valveV3, a flow meter S2, a pressure sensor S3, and a one-way valve V4 forpreventing backflow are provided on the flow channel L1. The flow ratecontrol valve V3 is electrically connected to the flow meter S2 and isconfigured so that the flow rate of ozone in the flow channel L1 can beadjusted based on the flow rate detected by the flow meter S2. Inaddition, a flow rate control valve V5 and a flow meter S4 are providedon the flow channel L3 and are electrically connected to each other sothat the flow rate of the wastewater W supplied from the wastewater tank6 to the microbubble generator 2 is adjusted by the flow rate controlvalve V5, based on the flow rate detected by the flow meter S4. A filterF3, an on-off valve V17, and a flow meter S4′ are provided on the flowchannel L4, and the flow rate of the flow channel L4 can be monitored bythe flow meter S4′. A flow meter S5 and an on-off valve V6 are providedon the flow channel L5. An on-off valve V7 and a filter F2 are providedon the flow channel L6 and are configured to be able to switch thesupply and stop of wastewater from the ozone oxidation unit 4 to thebiological treatment unit 5. In addition, an on-off valve V8 and aone-way valve V12 are provided on the flow channel L7 and are configuredto be able to switch the return and shutoff of wastewater from the ozoneoxidation unit 4 to the microbubble generator 2. In addition, an on-offvalve V9 is provided on the flow channel L3, and the supply of thewastewater W to the microbubble generator 2 can be controlled by theon-off valve V9.

In the above configuration, when the ozone generator 1 and themicrobubble generator 2 are operated while the on-off valves V6, V9, andV17 are opened to drive the suction pump 3, the wastewater W and ozoneare supplied to the microbubble generator 2 at flow rates in accordancewith the mixing ratio of the initial setting and the ozone mixedwastewater is introduced into the bottom inlet of the ozone oxidationunit 4. The supplied ozone mixed wastewater rises from a bottom parttoward a top part of the ozone oxidation unit 4, and sequentially passesthrough a plurality of catalyst beds C in the meantime, thereby theozone oxidation is promoted by the contact with the catalyst. Thewastewater in the ozone oxidation unit 4 can be discharged through theflow channel L6 or the flow channel L7 under pressure. The pressureinside the ozone oxidation unit 4 is monitored by a pressure sensor S11provided at the top.

As a measuring device which measures the amount of ozone in thewastewater that has passed through the catalyst bed C, an ozone meter S6is provided above the catalyst bed C in the ozone oxidation unit 4 todetect the residual ozone. The ozone meter S6 is electrically connectedto the on-off valves V7 and V9. When the remaining amount of ozone inthe wastewater to be detected is at the level that inhibitsmicroorganisms in the biological treatment unit 5, the on-off valves V7and V9 are closed to make the wastewater return from the ozone oxidationunit 4 to the microbubble generator 2 and circulate between themicrobubble generator 2 and the ozone oxidation unit 4. At the sametime, the flow rate control valve V3 of the flow channel L1 iscontrolled so that the flow rate of ozone supplied to the microbubblegenerator 2 is reduced. In other words, the ozone meter S6 and the flowrate control valve V3 configure an adjusting device to adjust the amountof ozone to be mixed with the wastewater, and the mixing ratio of ozoneis adjusted so that ozone in an amount that inhibits the microorganismsdoes not remain in the wastewater after the ozone oxidation. The changeamount in the flow rate of ozone under the control of the flow ratecontrol valve V3 may be reduced in accordance with the differencebetween the detection value of the ozone meter S6 and the level value,or may be a constant flow rate that is reduced stepwise. It is notedthat the mixing ratio of ozone to wastewater can also be adjusted bychanging a generation rate of ozone in the ozone generator 1 or a supplyrate of oxygen as a raw material. Therefore, the above-describedadjusting device may be configured by using a signal control of theozone generator or a regulating valve for regulating a supply flow rateof an oxygen source, instead of using the flow rate control valve V3. Inthe case where the remaining amount of ozone detected by the ozone meterS6 is less than the level that inhibits microorganisms, the on-offvalves V7 and V9 are opened. As a result, depending on the amount ofwastewater supplied from the wastewater tank 6, the wastewater isdischarged from the ozone oxidation unit 4 and is supplied from theozone oxidation unit 4 to the bottom part of the biological treatmentunit 5. Accordingly, if the water quality of wastewater is not changed,this state becomes a steady state, and the ozone oxidation treatment andthe biological treatment of the wastewater are stably continued. Ozonein an amount that inhibits microorganisms does not remain in thewastewater discharged from the ozone oxidation unit 4. The ozone meterS6 in FIG. 2 measures the dissolved ozone in the wastewater, but it maybe an ozone meter that measures the ozone concentration of the gas phaseon the wastewater. Then it is possible to convert from the ozoneconcentration of gas phase to ozone concentration in the wastewater.

The wastewater supplied to the biological treatment unit 5 rises fromthe bottom part toward the top part of the biological treatment unit 5,and passes through the biological beds B in the meantime. Since thewastewater supplied to the biological treatment unit 5 containshigh-concentration dissolved oxygen, the aerobic reaction bymicroorganisms proceeds. Oxygen is consumed as the treatment proceeds.Therefore, in the case where the microorganisms used in the biologicaltreatment unit 5 contain anaerobic microorganisms, if oxygen isexhausted, the reaction of the microorganisms is switched to theanaerobic reaction. In this case, the aerobic biological treatmentalways proceeds in the lower part of the biological bed, whereas theanaerobic biological treatment can proceed according to poor oxygenationin the upper part of the biological bed. After the biological treatment,the treated water W′ is discharged from the upper end of the biologicaltreatment unit 5 to the post-treatment water tank 7 through the flowchannel L8.

The wastewater treatment device 10 further has a flow channel L9 whichconnects the post-treatment water tank 7 to the flow channels L3 and L4,and a pump 8, a flow rate control valve V10, a filter F4, a flow meterS7, and a one-way valve V11 are provided on the flow channel L9, so thatthe treated water W′ of the post-treatment water tank 7 possibly returnsto the microbubble generator 2 through the flow channel L9 and the flowchannels L3 and L4. The flow rate control valve V10 is electricallyconnected to the flow meter S7 and controlled based on the flow ratedetected by the flow meter S4, and the flow rate of the treated water W′supplied to the microbubble generator 2 can be adjusted by a flow ratecontrol valve V5. In the case where the concentration of organicpollutants in the wastewater W is extremely high and there is a risk ofinterfering with the biological treatment, the wastewater W can beappropriately diluted using the treated water W′, so that the ozoneoxidation treatment and the biological treatment can be carried outwithout interference. It is appropriate to determine whether or not toperform the return of the treated water W′ based on the COD measurementvalue of the wastewater W. In addition, a branching path which isbranched from the flow channel L8 to supply the wastewater to thewastewater tank 6 may be provided so that the wastewater can be treatedagain when the COD measurement value of wastewater after the biologicaltreatment does not satisfy the drainage standard.

Since the heights of the biological treatment unit 5 and the ozoneoxidation unit 4 are different from each other and the water level inthe biological treatment unit 5 is lower than the water level in theozone oxidation unit 4, it is possible to supply the wastewater of theozone oxidation unit 4 to the biological treatment unit 5 by using thegravity action due to the difference in height of the water levelwithout using the power of the pump or the like. A water level gauge S8for detecting a liquid level is provided on the upper part of the ozoneoxidation unit 4 for the management such that the liquid level of thewastewater in the ozone oxidation unit 4 is maintained at a constantlevel when the wastewater is discharged from the ozone oxidation unit 4.

Water level gauges S9 and S10 are installed in the wastewater tank 6 andthe post-treatment water tank 7, respectively. The introduction of thewastewater W into the wastewater tank 6 and the discharge of the treatedwater W′ from the post-treatment water tank 7 are managed based on thedetection of the water level gauges S9 and S10, and the replenishment ofthe wastewater W and the discharge of the treated water W′ areappropriately performed to maintain the water level. On-off valves V13,V14, V15, V16, V17 and V18 are installed in order to drain water fromeach of the flow channels of the device and each of the ozone oxidationunit 4 and the biological treatment unit 5. These on-off valves areopened after the wastewater treatment, which enables, if necessary, toinspect and repair the device. These on-off valves are closed at thestart of the treatment.

In the wastewater treatment device described above, ozone is supplied inthe form of microbubbles, such that the gas-liquid mass transfer ofozone is improved and the rate of decomposition and reaction isimproved. Moreover, since the time for ozone to stay in the wastewateris long, the ozone utilization efficiency is remarkably high, and thegas phase ozone which is unused and released outside the wastewater isreduced. In addition, hydroxy free radicals are generated by ozoneoxidation using a catalyst, and the persistent organic pollutants areeasily decomposed, so that biodegradability of the wastewater isimproved. Furthermore, the reactivity of ozone is improved, so that theconcentration of dissolved oxygen in wastewater is increased and theefficiency of aerobic treatment in the biological treatment is improved.

Since ozone is generated by irradiation of ultraviolet rays or electricdischarge to oxygen, the ozone generator 1 is possibly configured usinga commercially available oxygen generating device. The oxygen generatingdevice is a device based on a concentration method such as those ofadsorptive separation (PSA) type, oxygen enriched membrane type andcryogenic separation type, and any type of oxygen generating device maybe used. In the oxygen generating device, oxygen which is separated andconcentrated from air is used as a raw material of ozone. The amount ofozone supplied from the ozone generator 1 can be adjusted by changingthe amount of oxygen which is generated from the ozone generatingdevice. The generation amount of ozone (that is, the supply amount ofozone) can be determined according to the water amount and the waterquality of the wastewater to be treated. Alternatively, instead of theoxygen generating device, ozone may be generated by using oxygen storedin a liquid oxygen tank, a curdle in which oxygen cylinders arecollected, or the like as an oxygen supply source.

The microbubble generator 2 is a gas-liquid mixer employing an OHRgas-liquid mixing manifold technology, and has an advantage that it issuitable for large-scale applications. By controlling the gas/watervolume ratio to 1/10 and setting a pre-tube pressure higher than 0.3MPa, it is possible to stably generate microbubbles having a diameterless than 50 μm. The microbubble generator 2 may be replaced withanother mixer such as another bubble generator, an inline mixer, etc.

The ozone oxidation unit 4 is configured of an airtight pressureresistant container having an operating pressure of less than 0.05 MPa,and the inside of the ozone oxidation unit 4 is subjected toanticorrosion treatment. In the above embodiment, an ozone oxidationcatalyst is used, and a catalyst bed C having a multistage structure inwhich particulate ozone oxidation catalyst is filled in each stage isdisposed in the tank. The ozone oxidation catalyst can be appropriatelyselected from various available particulate heterogeneous catalysts andused, and conditions such as the charged amount of the catalyst and thebed height can be determined according to the ozone oxidation catalystused.

The treatment time in the ozone oxidation unit 4 is set according to thewater quality of wastewater and is generally within one hour. TheBOD/COD value of wastewater is increased (BOD: biochemical oxygendemand) due to the reduction of persistent organic substances by theozone oxidation treatment, and the BOD/COD value in the treatedwastewater exceeds 0.3 while the concentration of dissolved oxygenexceeds 20 mg/L. Wastewater (wastewater/air mixture) that has undergonethe ozone oxidation is introduced into the bottom part of the biologicaltreatment unit 5 due to the liquid level difference, and no power isused.

In the above embodiment, a biofilter reactor is used as the biologicaltreatment unit 5, and a biological bed B having a multistage structureis configured by a filter-like carrier having a biofilm formed on thesurface thereof, but it is not limited to this configuration. Aconstituent material of the carrier may be any material as long as itdoes not inhibit the activity of microorganisms for the biologicaltreatment and it may include activated carbon, ceramics, minerals,various animal fibers and plant fibers such as wool, various chemicalfibers, and the like. Examples of minerals may include vermiculite,perlite, zeolite, and the like. Also, mold sand such as gravel, lavasand, chromite sand and zircon sand, etc., and mullite-based artificialsand (alumina-silica composite ceramic) which is the alternativeartificial sand, and the like can be used. The biological bed can beconfigured by using a particulate carrier as a filler, or a fibrousmaterial as forming a layered filter. As for the material that can bemolded and processed, it can be used in any form by processing. Thebiological bed B may be formed so that porosity is larger than 0.4. Thetreatment time (residence time of wastewater) in the biologicaltreatment unit 5 can generally be set to be 3 hours or longer. However,the setting of the treatment time can be shortened in accordance withthe COD value of the wastewater, the capacity of the treatment unit, andthe like. The aeration is unnecessary, and the treated water isdischarged as overflowing water from the top part. The activated sludge,which is microorganisms for general wastewater treatment, undergoes bothof the aerobic treatment and the anaerobic treatment depending on thetreatment conditions. Therefore, when the biological bed B isconstructed using such a microorganism group, similarly, the aerobictreatment and the anaerobic treatment can continuously proceed due tothe exhaustion of oxygen concentration. In this regard, if thebiological treatment unit 5 is divided into two parts for aerobictreatment and anaerobic treatment, and if microorganisms specialized foreach treatment are used in each part, the efficiency of the biologicaltreatment can be improved. In particular, the efficiency of the aerobictreatment can be improved by taking advantage of the high-concentrationdissolved oxygen in the wastewater discharged from the ozone oxidationunit 4. For this purpose, it is appropriate to determine theconstitution distribution of the biological bed B by investigating theconsumption trend of dissolved oxygen in the biological treatment unit 5in advance.

In this way, the ozone utilization efficiency in the ozone oxidationunit 4 can be increased to 99% or more, and the unused residual ozonecan be substantially reduced to zero. Also, since wastewater containingthe residual ozone can be prevented from affecting microorganisms byrestricting the supply to the biological treatment unit, gas treatmentfor ozone gas or the like is unnecessary. As the decomposition of thepersistent organic substances proceeds and the burden on the biologicaltreatment is reduced, the removal rate of organic pollutants can beachieved at least 30% or more to 50% or less based on COD. It ispossible to provide a wastewater treatment device which does not use apower source in the operation of the biological treatment unit and doesnot substantially require a power cost.

FIG. 3 shows another embodiment of the wastewater treatment device. Awastewater treatment device 10′ of FIG. 3 is configured to include arelease passage as a flow channel L7′ through which the wastewaterdischarged from the ozone oxidation unit 4 returns to the wastewatertank 6 (wastewater source). In this configuration, since the flow ratesof the flow channel L3 and the flow channel L4 are the same, a flowmeter S4′ of the flow channel L4 is omitted. Since the wastewatertreatment device is configured in the same manner as in FIG. 2 exceptfor the above points, a description thereof is omitted.

Also in the wastewater treatment device 10′ of FIG. 3, themicroorganisms of the biological treatment can be protected fromresidual ozone by utilizing the release passage according to thesituation of the wastewater after the ozone oxidation treatment. In theadjustment of the amount of ozone to be mixed with wastewater by usingthe regulating device, if ozone remains in the wastewater dischargedfrom the ozone oxidation unit 4, the supply of wastewater to thebiological treatment unit 5 is avoided by using the flow channels L7 andL7′. The wastewater flowing through the flow channel L7′ is supplied tothe wastewater tank 6 and indirectly supplied to the microbubblegenerator 2 via the wastewater tank 6 (wastewater source), to be mixedwith ozone. In the meantime, the mixing amount of ozone is optimized,and the wastewater discharged from the ozone oxidation unit 4 issupplied to the biological treatment unit 5. In the supply control ofwastewater in this embodiment, the wastewater in the wastewater tank 6is always supplied to the microbubble generator 2. While wastewatercirculates the microbubble generator 2 and the ozone oxidation unit 4,the supply destination of the wastewater discharged from the ozoneoxidation unit 4 in an amount corresponding to the amount of thewastewater supplied from the wastewater tank 6 is switched to either ofthe wastewater tank 6 or the biological treatment unit 5 in accordancewith the residual amount of ozone. Therefore, an on-off valve V9 of theflow channel L3 is not involved in this switching.

In FIG. 2 and FIG. 3, the supply control of wastewater by switching theon-off valve is configured so as to be automatically executable by theelectrical connection between the on-off valve and the flow meter or thesensor. However, of course, it is also possible to control the supply ofthe wastewater based on manual switching. When the water quality ofwastewater is stable, it is not necessary to perform the supply controlof wastewater after determining the treatment conditions in thewastewater treatment device.

EXAMPLES Treatment Example E1

As a result of examining the water quality of wastewater discharged froma chemical company, it was found that the COD concentration was about300 mg/L, the BOD/COD value was about 0.04, and the biodegradability wasextremely low. For this wastewater, the following treatment was carriedout using the wastewater treatment device as shown in FIG. 1. Thecatalyst bed arranged in the ozone oxidation unit was composed ofactivated carbon and the biological bed of the biological treatment unit5 was configured of a biofilter having a biofilm of aerobicmicroorganisms formed on the surface thereof.

The volume ratio of gas/water in the microbubble generator was set to1/10 and microbubbles were generated at a pre-tube pressure of 0.3 MPaor more, whereby wastewater in which ozone bubbles having a diameter of50 μm or less were dispersed was stably prepared and supplied to theozone oxidation unit (ozone/COD=2.6 mg/mg). As a result of setting theresidence time of wastewater in the ozone oxidation unit to be one hourand examining the water quality of the wastewater passing through thecatalyst bed, the COD was reduced to about 200 mg/L, the BOD/COD wasincreased to 0.30, and the concentration of dissolved oxygen exceeded 23mg/L. The COD load removal was 1.46 kg/(m³·d). The ozone concentrationof wastewater was about 2.5 mg/L, and the ozone utilization rateexceeded 95%.

This wastewater was introduced into the biological treatment unit as itwas, and after about 6 hours, the treated water overflowed from thebiological treatment unit. As a result of examining the water quality ofthe treated water, the concentration of dissolved oxygen was 10 mg/L ormore, and the COD concentration of the effluent treated water was stableand less than 100 mg/L.

Treatment Example E2

Using the device of FIG. 2, wastewater having a COD of 137 mg/L wassubjected to the following wastewater treatment. The catalyst bedarranged in the ozone oxidation unit was composed of activated carbonand the biological bed of the biological treatment unit 5 was configuredof a biofilter having a biofilm of aerobic microorganisms formed on thesurface thereof.

Wastewater and ozone were supplied to the microbubble generator 2 at amixing ratio of ozone and wastewater at which a ratio of ozone/COD was0.4 mg/mg to prepare ozone mixed wastewater, and the prepared ozonemixed wastewater was supplied to the ozone oxidation unit 4. As a resultof setting the residence time of the wastewater in the ozone oxidationunit 4 to be one hour and examining the water quality of wastewaterpassing through the catalyst bed C, the COD was reduced to about 95 mg/Land the concentration of dissolved oxygen was 23.6 mg/L. The ozoneconcentration of wastewater was about 1.5 mg/L, and the ozoneutilization rate was 98%.

This wastewater was introduced into the biological treatment unit 5 asit was, and after about 6 hours, the treated water overflowed from thebiological treatment unit 5. The COD concentration of the treated waterwas 75 mg/L, and the organic matter removal rate in the biologicaltreatment was 21% based on the COD.

Although the embodiments of the present disclosure have been describedabove with reference to the accompanying drawings, the presentdisclosure is not limited to such embodiments, and it is to beunderstood that various changes or modifications that can be conceivedby those skilled in the art in the scope described in the claims fallwithin the technical scope of the present disclosure.

The wastewater treatment device having good treatment efficiency isprovided, which can contribute to the prevention of environmentalpollution and the like by spreading treatment technology of industrialwastewater. In addition, it is possible to contribute to the effectiveutilization of resources by reducing the operation cost and the like ofthe device.

As there are many apparently widely different embodiments of thedisclosure that may be made without departing from the spirit and scopethereof, it is to be understood that the disclosure is not limited tothe specific embodiments thereof, except as defined in the appendedclaims.

What is claimed is:
 1. A wastewater treatment device, comprising: anozone generator which supplies ozone; a mixer which mixes ozone suppliedfrom the ozone generator with wastewater and supplies ozone mixedwastewater; an ozone oxidation unit which progresses ozone oxidation inthe ozone mixed wastewater while passing the ozone mixed wastewatertherethrough and discharges wastewater in which the ozone has beenconsumed; a biological treatment unit which has microorganisms forbiological treatment and performs the biological treatment on thewastewater discharged from the ozone oxidation unit using themicroorganisms; and an adjusting device which adjusts the amount ofozone to be mixed with the wastewater by the mixer so that ozone in anamount that inhibits the microorganisms of the biological treatment unitdoes not remain in the wastewater discharged from the ozone oxidationunit, wherein the ozone oxidation unit has a catalyst that promotes anozone oxidation reaction by contacting with the ozone mixed wastewater.2. The wastewater treatment device according to claim 1, wherein theadjusting device includes: a measuring device which measures the amountof ozone in the wastewater discharged from the ozone oxidation unit; anda regulating valve capable of regulating the amount of ozone to be mixedwith the wastewater by the mixer, and the regulating valve is adjustedbased on measurement by the measuring device in such a manner that theamount of ozone in the wastewater is lower than a level at which themicroorganisms are inhibited.
 3. The wastewater treatment deviceaccording to claim 2, further comprising: a release passage for avoidingthe supply of the wastewater to the biological treatment unit when theozone remains in the wastewater discharged from the ozone oxidationunit; and a control valve which stops the supply of the wastewater tothe biological treatment unit when the amount of ozone in the wastewateris equal to or higher than the level at which the microorganisms areinhibited, based on the measurement by the measuring device.
 4. Thewastewater treatment device according to claim 3, wherein the releasepassage is a return passage capable of supplying the wastewaterdischarged from the ozone oxidation unit to the mixer, and thewastewater flows through the return passage when the supply of thewastewater to the biological treatment unit is stopped by the controlvalve.
 5. The wastewater treatment device according to claim 2, furthercomprising: an ozone decomposing device which decomposes ozone remainingin the wastewater discharged from the ozone oxidation unit when ozoneremains in the wastewater discharged from the ozone oxidation unit. 6.The wastewater treatment device according to claim 1, wherein the mixerincludes a bubble generator, and ozone is dispersed in the ozone mixedwastewater in a state of bubbles.
 7. The wastewater treatment deviceaccording to claim 6, wherein the bubble generator is a microbubblegenerator which generates fine bubbles having a bubble diameter of 10 to50 μm.
 8. The wastewater treatment device according to claim 1, whereinthe ozone oxidation unit is configured in a multistage structure inwhich a plurality of catalyst beds on which the catalyst is supportedare stacked in a vertical direction, and is configured so that the ozonemixed wastewater sequentially passes through the plurality of catalystbeds while being introduced from a bottom part of the ozone oxidationunit and rising toward a top part of the ozone oxidation unit.
 9. Thewastewater treatment device according to claim 1, wherein a differencein height between the biological treatment unit and the ozone oxidationunit is provided so that a water level in the biological treatment unitis lower than that in the ozone oxidation unit, and the wastewater ofthe ozone oxidation unit is supplied to the biological treatment unitusing a gravity action due to the difference in height.
 10. Thewastewater treatment device according to claim 1, wherein the catalystpromotes the ozone oxidation reaction in which an organic substancecontained in the ozone mixed wastewater decomposes.
 11. The wastewatertreatment device according to claim 1, wherein the ozone oxidationreaction is promoted by a hydroxyl radical or an ozonide ion generatedfrom the ozone.
 12. The wastewater treatment device according to claim1, wherein the catalyst comprises a heterogeneous catalyst selected fromthe group consisting of metal oxides, metal-supported oxides, zeolites,and activated carbon, the metal oxides include at least one selectedfrom the group consisting of CoO, MoO₃, and MnO₂, and themetal-supported oxides include silica gel on which at least one metalselected from the group consisting of Co, Cu, Pb, Ru, Pt and Pd issupported.
 13. A wastewater treatment method, comprising: ozonegeneration that supplies ozone; mixing preparation for mixing the ozonesupplied by the ozone generation with wastewater to supply ozone mixedwastewater; ozone oxidation treatment in which ozone oxidation isallowed to proceed in the ozone mixed wastewater, using a catalyst thatpromotes an ozone oxidation reaction by contacting with the ozone mixedwastewater, to discharge the wastewater in which the ozone has beenconsumed; and biological treatment in which the wastewater after theozone oxidation treatment is biologically treated with microorganisms,wherein an amount of ozone mixed with the wastewater in the mixingpreparation is adjusted so that ozone in an amount that inhibits themicroorganisms of the biological treatment does not remain in thewastewater discharged from the ozone oxidation treatment.
 14. Thewastewater treatment method according to claim 13, wherein a ratio ofozone to be mixed with the wastewater is adjusted according to a flowrate of the wastewater supplied to the ozone oxidation treatment andwater quality of the wastewater so that an appropriate amount of ozoneis mixed with the wastewater in the mixing preparation.
 15. Thewastewater treatment method according to claim 13, which is applied toan advanced treatment for treating industrial wastewater containing apersistent organic substance.
 16. The wastewater treatment deviceaccording to claim 1, wherein the catalyst comprises a heterogeneouscatalyst selected from metal oxides, metal-supported oxides, platinumgroup metals, zeolites, and activated carbon.
 17. The wastewatertreatment device according to claim 16, wherein the metal oxides includeFe₂O₃, CoO, MoO₃, MnO₂, SiO₂, Al₂O₃ and TiO₂, and the metal-supportedoxides include silica gel and titania on each of which a metal selectedfrom Co, Cu, Pb, Ru, Pt and Pd is supported.
 18. The wastewatertreatment method according to claim 13, wherein the catalyst comprises aheterogeneous catalyst selected from metal oxides, metal-supportedoxides, platinum group metals, zeolites, and activated carbon.
 19. Thewastewater treatment method according to claim 18, wherein the metaloxides include Fe₂O₃, CoO, MoO₃, MnO₂, SiO₂, Al₂O₃ and TiO₂, and themetal-supported oxides include silica gel and titania on each of which ametal selected from Co, Cu, Pb, Ru, Pt and Pd is supported.